1. Field of the Invention
The present invention relates to an apparatus for controlling rotation speed of a synchronous reluctance motor and particularly, to an apparatus for controlling rotation speed of a synchronous reluctance motor capable of controlling rotation speed and torque of a motor by detecting input voltage and input current of a synchronous reluctance motor and estimating speed and position angle of a rotor, without using a sensor for detecting rotor position.
2. Description of the Background Art
Generally, for a conventional apparatus for controlling rotation speed of a synchronous reluctance motor, information of speed or flux of a motor is necessary in case of performing an instantaneous torque control and accordingly, sensors such as a tachometer, generator, resolver or pulse encoder to abstract the information of speed or flux of a motor.
However, since it is difficult to handle the above sensors, the sensors are very sensitive to noise and increase cost, recently, much research about sensorless vector control methods capable of controlling speed and torque without revising the speed according to the second resistance change of a motor has been conducted actively in overseas advanced enterprises. been conducted actively in overseas advanced enterprises.
FIG. 1 is a block diagram showing structure of a conventional apparatus for controlling rotation speed of a synchronous reluctance motor and as shown in the drawing, the conventional apparatus for controlling rotation speed of a synchronous reluctance motor includes a first comparator 11 for outputting speed error after comparing a speed reference value xcfx89r* and real rotor speed value xcfx89r, a speed control unit 12 for outputting electric current iqs* for reference torque after performing PI control for compensating the outputted speed error, a second comparator 13 for outputting current error after comparing the current for reference torque iqs* and current for real torque iqs, a flux reference generation unit 14 for referring the flux and outputting flux reference value xcexd* according to the real speed xcfx89r, a flux control unit 15 for outputting a current for reference flux ids* after performing PI control receiving the above outputted flux reference value xcexd*, a third comparator 16 for outputting a corresponding current error by comparing the electric current for the reference flux ids* and current for real flux ids, a current control unit 17 for outputting voltage Vds* for reference flux and voltage Vqs* for reference torque according to an output current of the second comparator 13 and third comparator 16, a three phase voltage generation unit 18 for receiving the voltage Vds* for reference flux, voltage Vqs* for reference torque and the real position angle of the rotor xcex8 from the integrator 22, converting into three phase voltages Vas, Vbs and Vcs of the fixed coordinate system and outputting the voltages, an inverter unit 19 for rotating the synchronous reluctance motor 20 by applying the three phase voltages Vas, Vbs and Vcs of the three phase voltage generation unit 18, a rotor position detection unit 21 for yielding the real speed by detecting rotation speed of the synchronous reluctance motor, an integrator 22 for yielding the real position angle of the rotor by integrating the real speed xcfx89r and a coordinate conversion unit 23 for receiving the two phase electric currents ias and ics detected in rotating the synchronous reluctance motor 20, converting the currents into the current ids for real flux and current iqs for real torque and outputting the converted currents.
Here, operation principle of the conventional apparatus for controlling rotation speed of a synchronous reluctance motor with reference to the accompanied drawings is as follows.
First, the first comparator 11 outputs speed error to the speed control unit 12 after comparing a speed reference value xcfx89r* and real rotor speed value xcfx89r detected from the rotor position detection unit 18 in rotating the synchronous reluctance motor 17. Then, the speed control unit 12 outputs electric current iqs* for reference torque after performing PI control for compensating the outputted speed error.
On the other hand, the flux reference generation unit 14 generates and outputs the flux reference value xcexd* to the flux control unit 15 and the flux control unit 15 outputs the current ids* for reference flux to third comparator 16 after performing PI control by receiving the above outputted flux reference value xcexd*.
The third comparator 16 outputs the corresponding current error to the current control unit 17 by comparing the electric current ids* for the reference flux generated and outputted according to the outputted flux reference value xcexd* and current ids for real flux outputted to the coordinate conversion unit 20. Then, the current control unit 17 generates the voltage Vds* for reference flux and voltage Vqs* for reference torque, which are respectively D-axis voltage and Q-axis voltage by receiving the current errors outputted from the second comparator 13 and third comparator 16 and outputs the voltages to the three phase voltage generation unit 15.
Here, a formula for yielding the voltage Vds* for reference flux and voltage Vqs* for reference torque is as follows:                                                                         V                d                            =                                                                    R                    s                                    ⁢                                      i                    d                                                  +                                                      L                    d                                    ⁢                                                            ⅆ                                              i                        d                                                                                    ⅆ                      t                                                                      -                                                      ω                    e                                    ⁢                                      L                    q                                    ⁢                                      i                    q                                                                                                                                          V                q                            =                                                                    R                    s                                    ⁢                                      i                    q                                                  +                                                      L                    d                                    ⁢                                                            ⅆ                                              i                        q                                                                                    ⅆ                      t                                                                      -                                                      ω                    e                                    ⁢                                      L                    d                                    ⁢                                      i                    d                                                                                                          Formula        ⁢                  xe2x80x83                ⁢        1            
Here, Vd, Vq are respectively components of D-axis and Q-axis of voltage, id, iq are respectively components of the D-axis and Q-axis of current, Rs is resistance of stator side and Ld, Lq are inductances of the D-axis and Q-axis.
Then, the three phase voltage generation unit 18 generates three phase voltages Vas, Vbs and Vcs of the fixed coordinate system using the voltage Vds* for reference flux, voltage Vqs* for reference torque and the real position angle of the rotor xcex8 from the integrator 22 and applies the voltages into the inverter unit 19 and the inverter unit 19 applying the three phase voltages Vas, Vbs and Vcs into the synchronous reluctance motor 20.
At this time, the rotor position detection unit 21 for detecting the rotor position of the synchronous reluctance motor 20 outputs the real rotation speed of the detected motor into the first comparator 11 and the integrator 22. Then, the integrator 22 yields the position angle of the rotor (xcex8) corresponding to the real position of the rotor by integrating the real speed and outputs the angle into the coordinate conversion unit 23 and three phase voltage generation units 18.
Therefore, the conventional synchronous reluctance motor controls rotation speed of the motor by repeatedly performing the above process.
However, the conventional apparatus with the above operation, includes a torque ripple due to harmonic wave components included in the detected fundamental wave of current frequency, switching dead time and the like and accordingly, harmonic wave components are included in the induced voltage. Therefore, a ripple is generated in an estimated-calculated rotation speed and accordingly, precise speed control was not possible. Also, it was difficult to handle the apparatus by using an encoder and hall-sensor of the rotor position detection unit.
Also, the conventional apparatus for controlling rotation speed of a synchronous reluctance motor has problems that the cost increases due to using a costly rotor position detection unit and low speed control can not be smoothly done in spite of excellent high speed control.
Therefore, the object of the present invention is to control a low speed area and high speed area separately to maintain precision of speed control according to variation of load in sensorless speed control for detecting rotor position of a synchronous reluctance motor.
Another object of the present invention is to provide an apparatus for controlling rotation speed of a synchronous reluctance motor capable of accurately controlling rotation speed of a motor where detection of a rotor position such as in a compressor in a refrigerator and air conditioner is difficult by enabling linear control of the inductance variation according to current change using magnetic modeling of the motor.
To achieve these and other advantages in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for controlling rotation speed of a synchronous reluctance motor, including a first comparator for outputting speed error after comparing a speed reference value and real rotor speed value of a synchronous motor, a speed control unit for outputting electric current for reference torque after performing PI control for compensating the outputted speed error, a second comparator for outputting current error after comparing the outputted electric current for reference torque and electric current for real torque, a flux reference generation unit for generating and outputting flux reference value, a third comparator for outputting flux error after receiving the above outputted flux reference value and comparing the flux reference value and real flux value, a flux control unit for outputting voltage for reference flux of the synchronous coordinate system after performing PI control receiving the above outputted flux error, a current control unit for generating and outputting voltage for reference torque after receiving the current error outputted from the second comparator, a synchronization/fixed coordinate conversion unit for receiving the above voltage for reference flux, voltage for reference torque and position angle of the rotor showing the real position of a rotor estimated in the high speed and low speed areas of the synchronous reluctance motor, converting the two voltages in the synchronous coordinate system into two voltages in the fixed coordinate system and outputting the voltages, a three phase voltage generation unit for converting the outputted two voltages of the fixed coordinate system into three phase voltages and outputting the voltages, an inverter unit for inverting the outputted three phase voltages and then outputting a three phase electric currents for driving the synchronous reluctance motor, a synchronous reluctance motor which is driven by being received the outputted three phase currents, a fixed/synchronization coordinate conversion unit for detecting two phase currents among the three phase currents outputted to the synchronous reluctance motor and then outputting the currents to the second and third comparators and a flux observer, the flux observer for receiving the outputted two phase currents and the two voltages of the fixed coordinate system outputted from the synchronization/fixed coordinate conversion unit and then outputting the corresponding flux, a position estimation unit for estimating the position angle of the rotor for high speed control of the motor and rotation speed of the rotor using the outputted flux, a low speed control unit for receiving the position angle of the rotor and rotation speed, and then estimating the position angle of the rotor for low speed control of the motor and outputting the angle to the synchronization/fixed coordinate conversion unit and a transient state stabilization unit for stabilizing a transient state which is generated according to the low speed control and speed control algorithm.
The foregoing and other, features, aspects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.